Journal . d through asmall rolling mill giving the cylindrical formation. The nickelsupporting wires also pass between a rolling mill, one rollerof which is serrated ; this mill is operated by hand and cutsthe wires off to a convenient length. The glass tubes carry-ing the wires are cut off to short lengths by a V-shaped emerywheel ; each one is then separately placed in the hollow spindleof a small lathe, a blow-pipe flame plays upon the protrudingend which in a semi-fused state forms a flange, being assistedby a hand tool. 48 SOME MODERN ENGINEERING PRACTICE IN AMERICA. Evacuation by Langmui
Journal . d through asmall rolling mill giving the cylindrical formation. The nickelsupporting wires also pass between a rolling mill, one rollerof which is serrated ; this mill is operated by hand and cutsthe wires off to a convenient length. The glass tubes carry-ing the wires are cut off to short lengths by a V-shaped emerywheel ; each one is then separately placed in the hollow spindleof a small lathe, a blow-pipe flame plays upon the protrudingend which in a semi-fused state forms a flange, being assistedby a hand tool. 48 SOME MODERN ENGINEERING PRACTICE IN AMERICA. Evacuation by Langmuir Pumps.—(Fig. 5.) There areten ovens, each of which will carry about fifty valves,but about forty at a time are sealed on to the glassmanifolds. Along the bottom of the oven are two rowsof gas jets which keep the temperature about 650° F.,during the time of the evacuation. Where the glass tubeieaves the oven, at the end where the pump is fixedit turns into a downward leg into which the necessary driers. Fig. for Fixing the be placed. The pumps are of a mechanical and mercuryvapour type ; each one having a duplex head in place of thesingle head usually provided, and the pumping operation hasbeen reduced from about four hours to about one and one-halfhours by reason of a special treatment which has been arrivedat as a result of considerable experimental work. Althoughit has been possible to obtain the prescribed blue glow test bydirect pumping and freezing, the time involved militated againstthis method as a commercial one and the valves as treatedcomply with the tests. Incidentally, a pressure of over can be applied to the anode, but this pressure maybe modified as advisability dictates. After the valveshave been removed from the ovens they are subjected to aspecial treatment to ensure the absence of blue glow, indicating SOME MODERN ENGINEERING PRACTICE IN AMERICA. 49
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